Project summary The long term goals of this proposal are to understand the control of bacterial DNA replication and the connections between replication and gene expression. Cell growth and propagation require duplication and segregation of chromosomal DNA. Cells have multiple mechanisms for regulating the initiation of replication and many have regulatory responses to perturbations in replication, often called checkpoints, which control cell cycle progression. Coupling gene expression and cell cycle progression to chromosome replication and integrity helps prevent the generation of cells with defective chromosomes. The coordination of genome duplication with cell cycle progression is also important for cellular differentiation and preventing uncontrolled cell growth. Many diseases, including cancers, result from aberrant regulation of replication and cell growth. In addition, microbial pathogenesis often depends on normal bacterial replication and growth in the host. This proposal focuses on several aspects of chromosome dynamics and gene expression in the Gram- positive bacterium Bacillus subtilis. We will use a variety of approaches and methodologies, both in vivo and in vitro, to characterize genes controlled in response to replication fork arrest, the role of DnaA, the replication initiator protein, in the transcriptional response to replication fork arrest, and the control of replication initiation and assembly of the replisome at an origin of replication in vivo. The fundamental principles and mechanisms controlling these processes are easily studied in B. subtilis using a combination of cell biological, genetic, molecular, physiological, biochemical, and bioinformatic approaches. Because many of the proteins involved in these processes are highly conserved, insights gained from our work with this relatively simple, experimentally accessible microbe, are likely to provide information regarding similar processes and homologous proteins in a wide variety of organisms, including many of the important Gram-positive pathogens. Learning more about the essential mechanisms governing chromosome replication and its effects on gene expression could lead to the identification of targets for the development of new antibiotics.